Generally, a motorcycle is provided with an engine unit mounted below a main tube extending backwardly from a head pipe, and a seat mounted upon a seat rail extending backwardly still further from the back end of the main tube. In the instance that a storage box compartment is required for storing a large commodity such as, for example, a helmet, it is possible to adopt an arrangement, such as, for example, by mounting the storage box upon the main tube and shifting the fuel tank to another location such as, for example, below the seat.
On the other hand, when maintenance is to be carried out for the engine unit and auxiliary machinery is arranged around it, the storage box tends to become an obstacle. More particularly, every time maintenance is to be carried out, it is necessary to dismount the storage box. The foregoing is especially true in the case of motorcycles which are comparatively large in size and in many cases provided with cowlings extending from the front portion of the engine unit to the opposite sides thereof, whereby the frequency dismounting of the storage box becomes high. Accordingly, it is required that the storage container box can be readily mounted and dismounted with respect to the motorcycle framework.
However, it is necessary to design the storage box so as not to be readily dismounted by means of an un-authorized person because the interior of the storage box is mainly used for personal matter or for storing things which are important and expensive.
It is also necessary for the storage box attaching device to be easily visible and readily accessible and operable so as not to provide an aesthetically poor outer appearance thereof.
In a related aspect, in the prior technology, since the rear wheel is disposed below the seat, the motorcycle is very compact with respect to available space. Therefore, there is a problem that, in connection with a fuel tank which is capable of having a sufficient capacity, it is difficult to define a configuration and an attaching device as well so as to dispose a fuel supply port and a fuel supply cock which are readily accessible and operative. The fuel tank is required to be provided with a reserve device comprising a reservoir tank and a cock for the changeover of the fuel, or a precaution device providing a reserve liquid level caution indicator, light, alarm, or the like for preventing the shortage or complete depletion of fuel. It is, however, ideal to provide a fuel gauge enabling the driver or operator to monitor the amount of stored fuel.
However, although it is possible to readily provide a fuel shortage prevention or monitoring means for the peculiarly configured fuel tank as mentioned above, it is mechanically as well as electrically difficult to manufacture and attach such a fuel gauge which is capable of continuously indicating the fuel storage condition between a full tank state and an empty state (F.rarw..fwdarw.E). Furthermore, it is virtually impossible to observe the liquid surface of the fuel through the fuel supply port after removal of the cap. Accordingly, since it is impossible for the driver to know how much fuel still remains within the fuel tank, such condition results in severe anxiety to the driver.